An engine of a hybrid vehicle may be started via a motor that propels the hybrid vehicle. In particular, a driveline disconnect clutch may be closed to transfer torque from the motor to the engine at a same time the motor is propelling the vehicle. The driveline disconnect clutch may be slipped such that a first side of the driveline disconnect clutch rotates at a different speed than a second side of the driveline disconnect clutch to reduce the possibility of driveline torque disturbances. However, driveline disconnect clutch losses may increase, thereby reducing driveline efficiency if the driveline disconnect clutch slips for longer than is desired. Further, if the disconnect clutch torque capacity is greater or less than is desired, an objectionable change in wheel torque during engine starting may be produced by closing the driveline disconnect clutch. Therefore, it would be desirable to provide a way of operating a driveline disconnect clutch to start an engine that reduces disconnect clutch losses and provides a smooth engine start.
The inventors herein have recognized the above-mentioned issues and have developed an operating method for a vehicle, comprising: adjusting a torque capacity of a driveline disconnect clutch responsive to an estimated torque to rotate an engine at a desired cranking speed and an additional torque that is based on a torque converter impeller speed.
By adjusting driveline disconnect clutch torque capacity responsive to an estimated amount of torque to rotate an engine at a desired cranking speed and torque converter impeller speed, it may be possible to provide the technical result of reducing driveline disconnect clutch losses. In particular, the torque capacity of the driveline disconnect clutch may be increased to transfer more torque to the engine than to rotate the engine at a cranking speed so that the engine may start sooner, thereby reducing an amount of time the driveline disconnect clutch slips. Further, in some examples, the torque capacity of the driveline disconnect clutch may be reduced after being increased in response to increasing driver demand torque so that wheel torque may increase with increasing driver demand torque. In these ways, it may be possible to reduce driveline losses and provide smoother wheel torque progression.
The present description may provide several advantages. Specifically, the approach may reduce driveline losses. In addition, the approach may reduce driveline disconnect clutch degradation via reducing an amount of time the driveline disconnect clutch slips. Further, the approach may adjust for various driving conditions so that driveline disconnect clutch slipping may be appropriate for a variety of driving conditions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.